# How to generate a new field from other fields without calculator
**URL:** https://discourse.paraview.org/t/how-to-generate-a-new-field-from-other-fields-without-calculator/17205
**Category:** ParaView Support
**Created:** [September 24, 2025, 3:26pm UTC](https://discourse.paraview.org/t/how-to-generate-a-new-field-from-other-fields-without-calculator/17205 "2025-09-24T15:26:03Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@DavidLarry](https://discourse.paraview.org/u/DavidLarry)
#### Post date: [September 24, 2025, 3:26pm UTC](https://discourse.paraview.org/t/how-to-generate-a-new-field-from-other-fields-without-calculator/17205/1 "2025-09-24T15:26:03Z")
Dear support,
I am trying to estimate the principal stress from stress and shear stress components using matrix resolution.
This type of resolution cannot be used in a calculator ad thus I wanted to do it using pvbatch:
1. loop over all cells
2. Solve the matrix for each cell
3. Add the result to a new field
4. Visualise the new field over the whole domain
Could anyone help me, especially regarding the creation of a new field (cell based) and the filling of said field?
Thank you
PS: long live Paraview
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [September 24, 2025, 3:30pm UTC](https://discourse.paraview.org/t/how-to-generate-a-new-field-from-other-fields-without-calculator/17205/2 "2025-09-24T15:30:39Z")
> [@DavidLarry](#):
>
> This type of resolution cannot be used in a calculator ad thus I wanted to do it using pvbatch:
You want to do that using a programmable filter đ
> **[6. Programmable Filter â ParaView Documentation 6.0.0 documentation](https://docs.paraview.org/en/latest/ReferenceManual/pythonProgrammableFilter.html)**
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### Author:  [@DavidLarry](https://discourse.paraview.org/u/DavidLarry)
#### Post date: [September 24, 2025, 4:42pm UTC](https://discourse.paraview.org/t/how-to-generate-a-new-field-from-other-fields-without-calculator/17205/3 "2025-09-24T16:42:53Z")
Hello Mathieu,
Thanks for the quick feedback, itâs a nice feature that I didnât know about.
So I gave it a try and I can recover the data I want using the examples.
The only issue I have then is using VTKArray with numpy, due to the format of the data:
How can I convert it to numpy array? I tried np.array on the VTKArray but it failed.
Thank you
Below the script I tried to use
##############################################
Code for âScriptâ
```auto
import numpy as np
input0 = inputs\[0\]
#Recover data
sigma_x = np.array(input0.CellData\[âsigma_xxâ\])
sigma_y = np.array(input0.CellData\[âsigma_yyâ\])
sigma_z = np.array(input0.CellData\[âsigma_zzâ\])
tau_xy = np.array(input0.CellData\[âsigma_xyâ\])
tau_yz = np.array(input0.CellData\[âsigma_yzâ\])
tau_xz = np.array(input0.CellData\[âsigma_xzâ\])
#Build the tensor
sigma_tensor = np.array(\[
\[sigma_x, tau_xy, tau_xz\],
\[tau_xy, sigma_y, tau_yz\],
\[tau_xz, tau_yz, sigma_z\]
\])
#Solve the coefficients
I1 = np.trace(sigma_tensor)
I2 = (sigma_x *sigma_y + sigma_y sigma_z + sigma_z sigma_x
- tau_xy\*\ ****2 - tau_yz** \*\*2 - tau_xz\*\*2)
I3 = np.linalg.det(sigma_tensor)
```
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### Author:  [@Lucas\_Givord](https://discourse.paraview.org/u/Lucas_Givord)
#### Post date: [September 26, 2025, 7:44am UTC](https://discourse.paraview.org/t/how-to-generate-a-new-field-from-other-fields-without-calculator/17205/4 "2025-09-26T07:44:54Z")
Note that the Yield Criteria filter could compute the principal stress (but not shear stress):
However there is some assumption regarding the tensor itself, see : [Pb with YieldCriteria Filter](https://discourse.paraview.org/t/pb-with-yieldcriteria-filter/16083)